Ertapenem N-Carbonyl Dimer Impurity

(4R,5S,6S)-3-(((3S,5S)-5-((3-((2S,4S)-4-(((4R,5S,6S)-2-carboxy-6-((R)-1-hydroxyethyl)-4-methyl-7-oxo-1-azabicyclo[3.2.0]hept-2-en-3-yl)thio)-2-((3-carboxyphenyl)carbamoyl)pyrrolidine-1-carbonyl)phenyl)carbamoyl)pyrrolidin-3-yl)thio)-6-((R)-1-hydroxyethyl)-4-methyl-7-oxo-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylic acid